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arXiv · 1609.07530

GRS 1739-278 observed at very low luminosity with XMM-Newton and NuSTAR

F. Fuerst·J. A. Tomsick·K. Yamaoka·T. Dauser·J. M. Miller·M. Clavel·S. Corbel·A. C. Fabian·J. Garcia·F. A. Harrison·A. Loh·P. Kaaret·E. Kalemci·S. Migliari·J. C. A. Miller-Jones·K. Pottschmidt·F. Rahoui·J. Rodriguez·D. Stern·M. Stuhlinger·D. J. Walton·J. Wilms
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Abstract

We present a detailed spectral analysis of XMM-Newton and NuSTAR observations of the accreting transient black hole GRS 1739-278 during a very faint low hard state at ~0.02% of the Eddington luminosity (for a distance of 8.5 kpc and a mass of 10 M_sun ). The broad-band X-ray spectrum between 0.5-60 keV can be well-described by a power law continuum with an exponential cutoff. The continuum is unusually hard for such a low luminosity, with a photon index of Gamma = 1.39 +/- 0.04. We find evidence for an additional reflection component from an optically thick accretion disk at the 98% likelihood level. The reflection fraction is low with R_refl = 0.043(+0.033,-0.023). In combination with measurements of the spin and inclination parameters made with NuSTAR during a brighter hard state by Miller and co-workers, we seek to constrain the accretion disk geometry. Depending on the assumed emissivity profile of the accretion disk, we find a truncation radius of 15-35 Rg (5-12 R_ISCO ) at the 90% confidence limit. These values depend strongly on the assumptions and we discuss possible systematic uncertainties.

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F. Fuerst, J. A. Tomsick, K. Yamaoka, T. Dauser, J. M. Miller, M. Clavel, S. Corbel, A. C. Fabian, J. Garcia, F. A. Harrison, A. Loh, P. Kaaret, E. Kalemci, S. Migliari, J. C. A. Miller-Jones, K. Pottschmidt, F. Rahoui, J. Rodriguez, D. Stern, M. Stuhlinger, D. J. Walton, J. Wilms. 2016-09-23. GRS 1739-278 observed at very low luminosity with XMM-Newton and NuSTAR. https://doi.org/10.3847/0004-637x%2F832%2F2%2F115

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